Uniaxial Stress Experiments and Magnetoelastic Interactions in Manganese Oxide

We have measured the thermal expansion and the N\'eel temperature of a single crystal of manganese oxide as a function of uniaxial stress applied along a (111) axis. It is shown that under well-defined experimental conditions, the antiferromagnetic-paramagnetic transition is of first order. The experimental results are used to study magnetoelastic interactions and magnetoelastic effects in manganese oxide.